The human eye often suffers from aberrations such as defocus and astigmatism that must be corrected to provide acceptable vision to maintain a high quality of life.
Correction of these defocus and astigmatism aberrations can be accomplished using a lens. The lens can be located at the spectacle plane, at the cornea (a contact lens or corneal implant), or within the eye as a phakic (crystalline lens intact) or aphakic (crystalline lens removed) intraocular lens.
The correction of these basic aberrations of defocus and astigmatism is generally limited to a single wavelength of light, typically in the middle of the visible spectrum. But the eye must function in a polychromatic environment that contains a wide range of wavelengths. For a refractive element such as a lens, the refracting power of the lens varies with wavelength. This is because the index of refraction of the lens material varies with wavelength. Generally, as wavelength increases, the index of refraction decreases. This variation in aberrations with wavelength is referred to as chromatic aberration.
Two methods that have been employed to combat the effects of chromatic aberration are wavelength band pass filters and diffractive lenses. Wavelength band pass filters use a dye to pass a given wavelength or narrow band of wavelengths and absorb the other wavelengths. An example is the “blue blocker” lens which passes wavelengths around green/yellow and absorbs blue and red wavelengths. Assuming defocus and astigmatism are corrected, the resulting retinal image is noticeably sharper since the chromatic aberration for the blue and red rays are reduced or eliminated. A negative of this approach is that the color information in the environment is significantly reduced.
A second method to combat chromatic aberration is the use of diffractive lenses. These lenses use step discontinuities to cause phase changes that reduce chromatic aberrations. A negative is that the step discontinuities also reduce the quality of the retinal image.
Our goal is to describe an ocular lens that overcomes the negative effects of the wavelength band pass filter lenses while maintaining its ability to reduce the negative effects of chromatic aberration. We term our lens the progressive chromatic aberration corrected ocular lens.